Variable permeability tuning system



y 4 w. R. KOCH 2,475,032

VARIABLE PERMEABILITY TUNI NG SY STEM Filed March 17, 1945 INVENTOR.W/NF/ELD R KOCH.

V W )fw A T TORNEY Patented July 5, 1949 VARIABLE PERMEABILITY TUNINGSYSTEM Winfield R. Koch, Haddonfield, N. J., assignor to RadioCorporation of America, a corporation of Delaware Application March 17,1945, Serial No. 583,214

4 Claims.

My present invention relates to a variable permeability tuning system,and more particularly to a permeability tuner in which the same coil andcore structure is utilized in multi-band receivers for tuning the samethrough different frequency ranges.

It is known, in order to effect permeability tuning in differentfrequency ranges, to shunt the main tuning inductance with a secondtuning reactance. If the shunting reactance is an inductance, thefrequency range capable of being covered at higher frequencies (due tothe lowered effective inductance of the two coils in parallel) will begreatly reduced as compared to the frequency range covered by the maintuning inductance alone at lower frequencies. If the shunting reactanceis a fixed capacitor, the L/C ratio becomes poor. According to thepresent invention, the construction is greatly simplified by providing,as the permeability tuned inductance, a pair ofwindings in bifilarrelation which are arranged to be connected in series and also inmagnetically aiding relation for the lower frequency range and inparallel, magnetically aiding relation for the higher frequency range.According to this ar rangement a wide range is covered for both bandswith a good L/C ratio in each case.

It is therefore one of the objects of the invention to provide, in amulti-band receiver, an improved tunable circuit which is adapted foruse in different bands and in which tuning in any of the bands isaccomplished by an adjustable ferromagnetic core without switching inauxiliary inductances or capacitors.

Another object of the invention is to provide a simple permeabilitytuner for multi-band receivers which employs a bifilar coil and anadjustable iron core cooperatively related therewith, the coil windingsbeing connected in series-aiding for one band and in parallel-aiding foranother band.

A further object is to provide a resonant circuit which comprises acapacitor, an inductor formed by winding two wires of equal sizesimultaneously side by side on a coil form, a magnetic core having anadjustable position for changing the inductance of said windings, and aswitch for connecting said windings in either series-aiding orparallel-aiding relation, the distributed capacity of said windings andthat of said capacitor having such relation that the resonantfrequencies obtainable with the switch in one position do notsubstantially overlap those obtainable with the switch in the otherposition.

The novel features characteristic of my invention are set forth withparticularity in the anpended claims. The invention itself, however,both as to its organization and mode of operation together with furtherobjects and advantages thereof, will best be understood by reference tothe following description taken in connection with the accompanyingdrawings in which:

Fig. 1 discloses in schematic fashion a permeability tuner constructedin accordance with the present invention, and

Figs. 2 and 3 show, respectively, the connections of the bi-filarwindings when switched to operate in their respective low frequency andhigh frequency bands.

Referring to Fig. 1 there is shown at l a tubular coil form of suitableinsulating material on which a pair of bi-filar windings 2, 3 are woundin the same direction. Preferably, the windings are single-layersolenoid windings having the same length and diameter, and with equalspacing between adjacent turns. The high potential end 4 of winding 2 isadapted to be connected to the signal grid 5 of an electron dischargetube 6 which may be either the radio frequency amplifier or theconverter stage of a radio receiver. This end of winding 2 is connectedalso to the movable arm I of a band change switch generally indicated bythe reference character 8. Associated with the switch arm I are a pairof contacts 9 and 10, the former being connected to the adjacent highpotential end ll of winding 3, while contact if] is blank. Highpotential end I I of winding 3 is connected also to a contact l2 of asecond switch arm 13 which is unicontrolled with switch arm I. A secondcontact [4 associated with arm I3 is connected to the low potential endl5 of winding 3 which is connected also to ground, and switch arm I3 isconnected to the low potential end It of winding 2.

The bi-filar windings 2 and 3 have associated with them an adjustableferro-magnetic tuning core I! which enters the coil form i at the lowpotential end of winding 3, suitable means, not shown, being providedfor the purpose of adjusting the axial position of the core and therebytuning the circuit to desired frequencies within each of the two bandshereinafter described. A trimmer condenser I8 is connected between thehigh potential end 4 of winding 2 and ground, or the low potential endI5 of winding 3.

For conditioning the tunable circuit (windings 2, 3 and capacitor l8)for operation in one frequency band, change switch 8 is actuated to theright, as viewed in Fig. 1, in which case, as shown in Fig. 2, thebi-filar windings are connected in series-aidin relation. Forconditioning the tunable circuit for operation in a higher frequencyband, change switch 8 is actuated to the left in which case, as shown inFig. 3, the bi-filar windings are connected in parallel-aiding relation.For effecting operation in still other frequency bands, there may beprovided one or more additional windings together with suitableswitching means for selectively connecting the coils in series-aiding orparallel-aiding relation. By the term aiding relation it is meant thatthe magnetic fields of the several coils are additive or in the samedirection.

For good Q (figure of merit), in series-aiding connection (Fig. 2), theinductor preferably should be wound on a low-loss form, with bare wire,spaced, and coated with low-loss coil dope. It should be noted that inthe series-aiding connection, the distributed capacity is much largerthan in the parallel-aiding connection because the distributed capacitybetween windings becomes effective. This may be useful in keeping thetwo ranges from overlapping, if capacitors are not switched whenchanging ranges. The number of turns is effectively changed 2-1 whichresults in almost 4-1 inductance change, in switching the connections.If a 9-1 inductance change occurs due to moving the core, correspondingto a 3-1 tuning frequency range, the shunting capacitor must be changed2.25 to 1 when changing connections, in order to avoid overlap. However,by proper circuit and coil design, the distributed capacity of the coilwill automatically give this change, without change in the shuntingcapacitor. With the parallel* aiding connection, the effective Q of thecoil is of course much better than if only one of the windings wereused. The tuning range, also, is greater with the parallel connectionthan if only one winding were used.

While I have shown and described a preferred embodiment of my invention,it will be understood that various modifications and changes will ocourto those skilled in the art without departing from the spirit and scopeof this invention. I therefore contemplate by the appended claims tocover any such modifications as fall within the true spirit and scope ofmy invention.

What I claim is:

1. A tuning device comprising a pair of inductance coils ofsubstantially equal inductive value and coaxially arranged on aninsulating form in bifilar relation, single means for tuning said deviceover either of two frequency bands, and switch means for selectivelyconnecting said coils in series-aiding relation with a substantialdifference in potential between adjacent turns of the coils,respectively, for operating the device in one frequency band and inparallel-aiding relation for operating the device in a differentfrequency band.

2. A permeability tuning device comprising a pair of windings wound inbifilar relation on an insulating form, a magnetic core axially movablewithin said form, and switch means for selectively connecting saidwindings in series-aiding relation with a substantial difference inpotential between adjacent turns of the windings, respectively, foroperating the device in one frequency band and in parallel-aidingrelation for operating the device in a different frequency band.

3. A permeability-tuned circuit adapted for use in multi-band radioreceivers, comprising a pair of coaxially arranged windings wound inbifilar relation on an insulating form in the same direction, a magneticcore axially movable within said form, switch means and connectionstherefrom to the winding terminals whereby in one position of saidswitch means the windings are connected in series-aiding relation with asubstantial difference in potential between adjacent turns of thewindings, respectively, for conditioning the circuit to be tuned throughone frequency band by adjustment of said magnetic core, and in anotherswitch position the windings are connected in parallel-aiding relationfor conditioning the circuit to be tuned through a different frequencyband by adjustment of said magnetic core.

4. A permeability tuned circuit as defined in claim 3, wherein thewindings whether connected in series-aiding or in parallel-aiding areshunted by the same fixed trimmer capacitor, said capacitor beingconnected permanently between a high potential terminal of one of saidwindings and a low potential terminal of the other of said windings.

WINFIELD R. KOCH.

REFERENCES CITED The following referenlces are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,639,044 Mansbridge Aug. 16,1927 2,095,420 Polydorafi Oct. 12, 1937 2,111,373 Schaper Mar. 15, 19382,131,976 Schaper Oct. 4, 1938 2,149,336 Darnell Mar. 7, 1939 2,163,051Miller June 20, 1939 2,255,680 Sands et a1. Sept. 9, 1941 2,291,780Witthoft Aug. 4, 1942 2,320,483 Stocker June 1, 1943 2,322,722 WentworthJune 22, 1943 2,334,670 DeCola Nov. 16, 1943 2,368,857 McClellan Feb. 6,1945 2,375,911 Foster May 15, 1945

